The statements in this section merely provide background information related to the present disclosure. Accordingly, such statements are not intended to constitute an admission of prior art.
Foundry sand is a quartz sand used in a process to refine and form molten metal into usage forms. The metal can be iron or other metals. Foundry sand can be combined with a bonding agent to aid the sand in retaining a shape, including clay or other chemical agents, and the sand can be formed into a mold to receive molten metal in a casting process. The foundry sand can include other additives to change properties of the sand. The molten metal is allowed to cool in the mold, and once the metal is cooled enough to retain its shape, the foundry sand can be separated from the metal. The foundry sand can be reused a number of times. However, the composition of the foundry sand mixture is changed through repeated casting cycles, and eventually the foundry sand must be removed from service and new foundry sand introduced. Foundry sand that can no longer be used is considered waste foundry sand. Waste foundry sand can be found to have other minerals included for the purpose of hardening. It can be recycled internally, but at some point the value is expended. The final waste foundry sand can also have metallic substances incorporated as a by-product of the metal casting process. One estimate includes 6 to 10 million tons of waste foundry sand being generated every year.
Frac sand is a particular grade of quartz sand, specified to a particular shape and size. Frac sand is useful in a number of applications, including in the petroleum industry wherein frac sand is injected into an oil well for the purpose of maximizing the total output of the well.
Foundry sand and frac sand can be produced at the same mines and may be produced from the same raw material. They are a silica/quartz mineral that is unique in shape, chemistry and physical properties. Frac sand has particular requirements that the sand particles must meet for sphericity, roundness, gradation and crush resistance. One primary difference between materials used for foundry sand and for frac sand is gradation requirements. The foundry sand has a wider acceptable gradation range.
Disposal of waste foundry sand is known to include uses wherein the waste foundry sand is used as filler. Civil engineering applications use waste foundry sand as landfill or material to build up a desired embankment. In this use, waste foundry sand is essentially treated as inert waste. The value of fresh foundry sand greatly exceeds the value of landfill for civil engineering uses. The value of frac sand greatly exceeds the value of landfill for civil engineering uses.